Porous silicon based on multilayer dielectric-grating optical sensors with enhanced biosensing

This paper reports on the use of a novel all-porous-silicon configuration consisting of a surface grating and a high-reflectivity quarter-wave stack, arranged as both an all-porous-silicon grating diffractive device, and a highly sensitive and inexpensive biosensor. The diffraction efficiency of the top surface grating in this structure can be considerably improved for biosensing. Moreover, a porous-silicon high-reflectivity multilayer can not only prevent the signal energy from radiating to the substrate, but also increase the internal surface area of the sensing platform for detecting more probing molecules. When 3-aminopropyltriethoxysilane (APTES) was employed as a probing molecule, the sensitivity of the proposed structure increased up to 1 order higher than the porous-silicon diffraction-grating biosensors without a high-reflectivity quarter-wave stack. It has been shown by experimentation that before and after the APTES, −3-order diffraction efficiency changes from 1.30 × 10 −3 to 1.25 × 10 −4 . Excellent agreement is achieved between the experimental results and simulations based on the rigorous coupled-wave analysis.